The proposed studies analyze neural and hormonal interactions in the control of sexual behavior (particularly the lordosis posture) in female rats. The intensity of lordosis (the extent of dorsiflexion of the back) can be increased either by increasing estrogen dosage or by increasing the intensity of sensory stimulation; thus the two factors are interchangeable. Vaginal stimulation, which normally facilitates lordosis, is so potent a stimulus for lordosis, that it can elicit lordosis even in ovariectomized, hormone-untreated rats. Thus, the neural systems involved in lordosis remain functional in the absence of estrogen. By increasing responsiveness to sensory stimulation by removing the septum, lordosis responsiveness was markedly enhanced even in the absence of ovarian hormones. Furthermore, vaginal stimulation, in addition to facilitating lordosis (an extensor-dominated reflex) also can completely block withdrawal reflexes (flexor-dominated reflexes), the latter even in spinal-transected rats. We are investigating the nature of this visceral stimulus which "gates" somatic activity. In studying this neural mechanism by which vaginal stimulation blocks withdrawal reflexes, we found that thalamic neuronal responses to painful stimulation were markedly or totally abolished by vaginal stimulation, while responses to tactile stimulation were unaffected. A behavioral study confirmed this pain blockage effect, for vocalizations in response to tail shocks were abolished by vaginal stimulation. The lordosis-facilitating and pain-blocking effects of vaginal stimulation could be explained by convergence of visceral vaginal and somatic afferent neurons from the flanks on the same spinal neurons. Their activity could summate in facilitating lordosis and somatic and/or visceral afferent activity could close a pain "gate." In addition to examining neural-hormonal interactions, these studies may elucidate the neural bases of visceral-somatic interactions, referred pain, and acupuncture.